The invention relates in general to inertial switches and in particular to small electro-mechanical inertial switches.
Acceleration detectors for commercial and military uses are known. Commercial uses include detecting impacts of colliding objects, detecting changes in vehicle speed, and detecting vibration events. Military uses include detecting impact of a munition with a target, detecting launch of a munition from a gun, and detecting the spin of a munition. Examples of acceleration detectors include accelerometers and threshold contact switches.
Some acceleration detectors are single direction, mass-spring systems, in which a mass moves relative to an internal sensing element. In the case of accelerometers, a change in electrical voltage corresponding to the position of the mass provides information about the acceleration or G-level. In the case of a threshold contact switch, an open state may indicate that the mass has not moved, and a closed state may indicate that the mass has moved and closed a gap, due to an external acceleration. The mass movement (or lack thereof) may indicate that the predetermined G-level has or has not been exceeded.
Both accelerometers and threshold contact switches may be used in fuzing applications. An advantage of a threshold contact switch, compared to an accelerometer, is that a threshold contact switch may require no continuous electric power or signal processing. The absence of power and processing may reduce the complexity of the fuze electronics. For a contact switch, only two contacts may need to be monitored to determine switch closure. The mechanical nature of the contact switch may allow acceleration thresholds to be fixed to a predetermined level by adjusting mechanical features internal to the switch. The adjustable mechanical features may include, for example, gaps, springs, masses, and volumes.
U.S. Pat. No. 6,765,160 (hereinafter '160) issued on Jul. 20, 2004 to Robinson discloses an omnidirectional microscale impact switch. The '160 switch may not have equal sensitivity or response for all azimuths in the x-y plane. The pathways for the electrical signals in the '160 switch may not allow for rapid solder flow mounting on a printed circuit board. In addition, the substrate etching needed to create a z-axis gap may be time-consuming and/or impractical. The metal-pattern required for the z-axis contact electrode may also be time-consuming and/or difficult to create in the etched substrate trench. A need exists for an improved triaxial MEMS acceleration switch.